Rainbow Electronics DS1680 - Manual (Page 3)

DS1680
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SIGNAL DESCRIPTIONS
V
CC
, GND (Digital Supply and Digital Ground) – DC power to the RTC, watchdog, X and Y drivers,
and power-switching circuitry is provided to the device on these pins.
V
BAT
(Backup Power Supply) – Battery input for standard 3V lithium cell or other energy source.
SCLK (Serial Clock Input) – SCLK is used to synchronize data movement on the serial interface.
I/O (Data Input/Output) – The I/O pin is the bidirectional data pin for the 3-wire interface.
CS (Chip Select) – The chip-select signal must be asserted high during a read or a write for
communication over the 3-wire serial interface.
V
CCO
(External SRAM Power Supply Output) – This pin is internally connected to V
CC
when V
CC
is
within nominal limits. However, during power-fail V
CCO
is internally connected to the V
BAT
pin.
Switchover occurs when V
CC
drops below V
CCSW
.
INT (Interrupt Output) – The INT pin is an active-high output of the DS1680 that can be used as an
interrupt input to a microprocessor. The INT output remains high as long as the status bit causing the
interrupt is present and the corresponding interrupt-enable bit is set. The INT pin operates when the
DS1680 is powered by V
CC
or V
BAT
.
CEI (SRAM Chip-Enable Input) – CEI must be driven low to enable the external SRAM.
CEO (SRAM Chip-Enable Output) – Chip-enable output for SRAM.
PFI (Power-Fail Input) – Power- fail comparator input. When PFI is less than 1.25V,
PFO goes low;
otherwise PFO remains high. Connect PFI to GND or V
CC
when not used.
PFO (Power-Fail Output) – Power-fail output goes low and sinks current when PFI is less than 1.25V;
otherwise PFO remains high.
SI (Strobe Input) – The strobe input pin is used in conjunction with the watchdog timer. If the ST pin is
not driven low within the watchdog time period, the RST pin is driven low.
RST (Reset) – The RST pin functions as a microprocessor reset signal. This pin has an internal 47k
Ω
pullup resistor.
X1, X2 – Connections for a standard 32.768kHz quartz crystal. For greatest accuracy, the DS1680 must
be used with a crystal that has a specified load capacitance of 6pF. There is no need for external
capacitors or resistors. Note: X1 and X2 are very high- impedance nodes. It is recommended that they and
the crystal be guard-ringed with ground and that high- freque ncy signals be kept away from the crystal
area. For more information about crystal selection and crystal layout considerations, please consult
Application Note 58, “Crystal Considerations with Dallas Real-Time Clocks.” The DS1680 will not
function without a crystal.